The present invention is concerned with the structure and application of a variable leakage transformer or a variable voltage transformer.
A transformer has, in general, a magnetic core having a closed magnetic path, a primary and secondary winding wound on said magnetic core, and all the input power applied to the primary winding is provided at the output of the secondary winding except for a small amount of loss in the transformer. In this case, the output voltage V.sub.2 across the secondary winding is EQU V.sub.2 =(n.sub.2 /n.sub.1).times.V.sub.1,
where V.sub.1 is the voltage across the primary winding and n.sub.1 and n.sub.2 are the number of windings of the primary and secondary windings, respectively.
When we want to control the output power of the transformer, a controllable switching device such as a SCR (Silicon Controlled Rectifier) or a transistor must be employed at the output of the transformer. In said controllable switching device, the pulse width during each cycle is varied by controlling the conducting time of the switching element (SCR). However, a prior controllable switching device has the disadvantage that the circuit is very complicated and the price of the device is rather high.
Another prior art device for controlling an AC power source is a magnetic amplifier, in which a saturable reactor is inserted between the power source and the load, and by controlling the reactor, the power transferred from the source to the load is controlled. However, a magnetic amplifier has the disadvantage that the voltage across the load must be the same as that of the power source, and the saturable reactor does not function as a variable-voltage transformer.